In fuel cell-supported transportation systems, chemical reformers are used for obtaining the required hydrogen from hydrocarbon-containing fuels.
All of the substances needed by the reformer to produce hydrogen, such as air, water and fuel, are ideally supplied to the reformer in the gaseous state. However, since the fuels, such as methanol or gasoline and water, are preferably stored onboard the transportation system in liquid form, they must be heated so as to be vaporized shortly before being fed into the reformer. This requires a pre-evaporator capable of providing adequate quantities of gaseous fuel and water vapor, the waste heat of the reformer normally being used for vaporization.
Since the hydrogen is normally consumed immediately, chemical reformers must be capable of adjusting the production of hydrogen to the demand without delay, e.g. in response to load changes or during start phases. Especially in the cold start phase, additional measures must be taken, since the reformer does not provide any waste heat. Conventional evaporators are not capable of generating adequate quantities of gaseous reactants without delay. It is therefore practical to introduce the fuel into the reformer in a finely divided form with the aid of an atomization device, in which case, provided that there is a sufficient supply of heat, the vaporization process is improved by the large surface area of the finely divided fuel. Devices for reforming fuels are described, for example, in U.S. Pat. No. 3,971,847. According to this reference, the fuel is metered by metering devices, located relatively far away from the reformer, via long supply lines into a temperature-adjusted substance stream and is dispersed via a metering aperture at the end of the supply line into the substance stream which flows to the location of the actual reforming process.
A particularly disadvantageous feature in the devices described in the above-mentioned document is the fact that the long supply lines result in delays and inaccuracies in fuel metering, especially in the case of sharp load changes or warm start phases. If fuel metering is resumed following a stop phase while the fuel is evaporating under the temperature influence from the supply line (for example), this results in a delayed metering of fuel into the temperature-adjusted substance stream and to the reforming process, because the dead-space volume in the supply line first has to be replenished. The same problem arises in the case of a particularly small load. Furthermore, long supply lines stand in the way of compact construction while increasing proneness to error and assembly cost. The use of high fuel pressures for improved atomization has a direct effect on the apportioned fuel quantity.